Throughout much of man's naval history he has sought more efficient means of sailing for reasons among others of going faster, providing more comfort, and having broader access to shallow areas of water. A significant gain came with the elimination of ballast and its attendent disadvantages of unusable displacement and extra draft. The progression to floats or pontoons instead of ballast to counteract the force of the wind added one more advantage to those of speed and manuverability. It reduced the heeling angle of a sailboat and made life on board more comfortable. These new craft took on two major forms: trimarans, which utilize a main hull with floats on each side, and catamarans, which eliminate the middle hull entirely and rely on the floats alone for support.
With the floats came new problems, however. The increased overall beam (width) and necessary structure of attachment exposed more area to action and loads from the sea. The considerable stresses imposed on the floats and connecting structure under storm conditions has caused the breakup of a number of craft and the emphasis on light weight has sometimes gone counter to the desire for strength.
Forces at work on these multi-hull craft have not been sufficiently analysed nor float attachment superstructures designed which accurately and efficiently resist the stresses which they encounter. A boat in a seaway is subject to many diverse forces and loads. As referred to here roll is a transverse movement about the fore and aft centerline axis of the boat, yaw is lateral movement about the vertical centerline axis, and pitch is a longitudinal movement about the beam axis horizontally perpendicular to the fore and aft centerline. In a multi-hull boat the means for countering roll is the floats which effect a broad base to resist the side heeling forces. Pitch is countered by the bouyancy of the ends of both floats and, if applicable, main center hull. Yaw is countered by a combination of the other two means. Traditionally the load carrying connecting members have been spars or solid decking running transversely from float to float. In neither of these methods is any emphasis given to diagonal bracing.
Sea conditions, in reality, rarely put the craft in purely defined parallel or right angle to the centerline motion or loads. Instead the forces add in a resultant vector of varying angles. A multi-hull not only carries these loads over its length and width but diagonally between the opposite tips of its seperate floats, as when the bow of one and the stern of the other are each supported by wave crests with a trough in betweem. As a crest passes from bow to stern so does the loading and, in fact, acts through a complete 360.degree. range. The traditional transverse wing deck or strut frame crossing from float to float at a right angle to the centerline is not stable in a diagonal or three dimensional axis. The floats and edges of this connecting structure form a parallelogram, instable in either a horizontal or vertical centerline plane. It is necessary that this structure connecting the parallel hulls have three dimensional integrity, free from warping or shear.